1.IMU模式与非IMU模式下REDO的区别

1.1.IMU模式

REDO RECORD - Thread:1 RBA: 0x000004.0000000b.0010 LEN: 0x0374 VLD: 0x0d //RBA: 0x000004.0000000b.0010 日志文件号4+块号64+偏移量10

SCN: 0x0000.04fd17af SUBSCN: 1 11/06/2016 04:32:47

CHANGE #1 TYP:2 CLS:1 AFN:4 DBA:0x01000a77 OBJ:91779 SCN:0x0000.04fd177c SEQ:1 OP:11.19 ENC:0 RBL:0

KTB Redo

op: 0x11 ver: 0x01

compat bit: 4 (post-11) padding: 1

op: F xid: 0x000a.00d.00007207 uba: 0x00c1198a.0242.30

Block cleanout record, scn: 0x0000.04fd17a9 ver: 0x01 opt: 0x02, entries follow...

itli: 1 flg: 2 scn: 0x0000.04fd177c

Array Update of 1 rows:

tabn: 0 slot: 0(0x0) flag: 0x2c lock: 2 ckix: 0

ncol: 2 nnew: 1 size: 0

KDO Op code: 21 row dependencies Disabled

xtype: XAxtype KDO_KDOM2 flags: 0x00000080 bdba: 0x01000a77 hdba: 0x01000a72

itli: 2 ispac: 0 maxfr: 4858

vect = 3

col 1: [ 5] 41 41 41 41 41

CHANGE #2 TYP:0 CLS:35 AFN:3 DBA:0x00c00110 OBJ:4294967295 SCN:0x0000.04fd1783 SEQ:2 OP:5.2 ENC:0 RBL:0 //CLS:35，大于16，对UNDO段的操作，OP:5.2 事务对UNDO段的操作，存放修改前值

ktudh redo: slt: 0x000d sqn: 0x00007207 flg: 0x0012 siz: 168 fbi: 0

uba: 0x00c1198a.0242.30 pxid: 0x0000.000.00000000

CHANGE #3 TYP:0 CLS:1 AFN:4 DBA:0x01000a77 OBJ:91779 SCN:0x0000.04fd17af SEQ:1 OP:11.19 ENC:0 RBL:0

KTB Redo

op: 0x02 ver: 0x01

compat bit: 4 (post-11) padding: 1

op: C uba: 0x00c1198a.0242.31

Array Update of 1 rows:

tabn: 0 slot: 1(0x1) flag: 0x2c lock: 2 ckix: 0

ncol: 2 nnew: 1 size: 0

KDO Op code: 21 row dependencies Disabled

xtype: XAxtype KDO_KDOM2 flags: 0x00000080 bdba: 0x01000a77 hdba: 0x01000a72

itli: 2 ispac: 0 maxfr: 4858

vect = 3

col 1: [ 5] 42 42 42 42 42

CHANGE #4 TYP:0 CLS:35 AFN:3 DBA:0x00c00110 OBJ:4294967295 SCN:0x0000.04fd17af SEQ:1 OP:5.4 ENC:0 RBL:0

ktucm redo: slt: 0x000d sqn: 0x00007207 srt: 0 sta: 9 flg: 0x2 ktucf redo: uba: 0x00c1198a.0242.31 ext: 2 spc: 1276 fbi: 0

CHANGE #5 TYP:0 CLS:36 AFN:3 DBA:0x00c1198a OBJ:4294967295 SCN:0x0000.04fd1783 SEQ:3 OP:5.1 ENC:0 RBL:0

ktudb redo: siz: 168 spc: 1572 flg: 0x0012 seq: 0x0242 rec: 0x30

xid: 0x000a.00d.00007207

ktubl redo: slt: 13 rci: 0 opc: 11.1 [objn: 91779 objd: 91779 tsn: 4]

Undo type: Regular undo Begin trans Last buffer split: No

Temp Object: No

Tablespace Undo: No

0x00000000 prev ctl uba: 0x00c1198a.0242.2d

prev ctl max cmt scn: 0x0000.04fd1109 prev tx cmt scn: 0x0000.04fd1133

txn start scn: 0x0000.04fd178c logon user: 84 prev brb: 12654980 prev bcl: 0 BuExt idx: 0 flg2: 0

KDO undo record:

KTB Redo

op: 0x03 ver: 0x01

compat bit: 4 (post-11) padding: 1

op: Z

Array Update of 1 rows:

tabn: 0 slot: 0(0x0) flag: 0x2c lock: 0 ckix: 0

ncol: 2 nnew: 1 size: 0

KDO Op code: 21 row dependencies Disabled

xtype: XAxtype KDO_KDOM2 flags: 0x00000080 bdba: 0x01000a77 hdba: 0x01000a72

itli: 2 ispac: 0 maxfr: 4858

vect = 3

col 1: [ 5] 61 61 61 61 61

CHANGE #6 TYP:0 CLS:36 AFN:3 DBA:0x00c1198a OBJ:4294967295 SCN:0x0000.04fd17af SEQ:1 OP:5.1 ENC:0 RBL:0

ktudb redo: siz: 124 spc: 1402 flg: 0x0022 seq: 0x0242 rec: 0x31

xid: 0x000a.00d.00007207

ktubu redo: slt: 13 rci: 48 opc: 11.1 objn: 91779 objd: 91779 tsn: 4

Undo type: Regular undo Undo type: Last buffer split: No

Tablespace Undo: No

0x00000000

KDO undo record:

KTB Redo

op: 0x02 ver: 0x01

compat bit: 4 (post-11) padding: 1

op: C uba: 0x00c1198a.0242.30

Array Update of 1 rows:

tabn: 0 slot: 1(0x1) flag: 0x2c lock: 0 ckix: 0

ncol: 2 nnew: 1 size: 0

KDO Op code: 21 row dependencies Disabled

xtype: XAxtype KDO_KDOM2 flags: 0x00000080 bdba: 0x01000a77 hdba: 0x01000a72

itli: 2 ispac: 0 maxfr: 4858

vect = 3

Array Update of 1 rows:

tabn: 0 slot: 0(0x0) flag: 0x2c lock: 0 ckix: 0

ncol: 2 nnew: 1 size: 0

KDO Op code: 21 row dependencies Disabled

xtype: XAxtype KDO_KDOM2 flags: 0x00000080 bdba: 0x01000a77 hdba: 0x01000a72

itli: 2 ispac: 0 maxfr: 4858

vect = 3

col 1: [ 5] 61 61 61 61 61

CHANGE #6 TYP:0 CLS:36 AFN:3 DBA:0x00c1198a OBJ:4294967295 SCN:0x0000.04fd17af SEQ:1 OP:5.1 ENC:0 RBL:0

ktudb redo: siz: 124 spc: 1402 flg: 0x0022 seq: 0x0242 rec: 0x31

xid: 0x000a.00d.00007207

ktubu redo: slt: 13 rci: 48 opc: 11.1 objn: 91779 objd: 91779 tsn: 4

Undo type: Regular undo Undo type: Last buffer split: No

Tablespace Undo: No

0x00000000

KDO undo record:

KTB Redo

op: 0x02 ver: 0x01

compat bit: 4 (post-11) padding: 1

op: C uba: 0x00c1198a.0242.30

Array Update of 1 rows:

tabn: 0 slot: 1(0x1) flag: 0x2c lock: 0 ckix: 0

ncol: 2 nnew: 1 size: 0

KDO Op code: 21 row dependencies Disabled

xtype: XAxtype KDO_KDOM2 flags: 0x00000080 bdba: 0x01000a77 hdba: 0x01000a72

itli: 2 ispac: 0 maxfr: 4858

vect = 3

col 1: [ 5] 62 62 62 62 62

1.2 非IMU模式

REDO RECORD - Thread:1 RBA: 0x000006.00000002.0010 LEN: 0x0204 VLD: 0x05

SCN: 0x0000.04fd31be SUBSCN: 1 11/06/2016 05:06:27

CHANGE #1 TYP:0 CLS:23 AFN:3 DBA:0x00c000b0 OBJ:4294967295 SCN:0x0000.04fd3151 SEQ:1 OP:5.2 ENC:0 RBL:0

ktudh redo: slt: 0x0014 sqn: 0x0000708a flg: 0x0012 siz: 168 fbi: 0

uba: 0x00c1a662.02f9.27 pxid: 0x0000.000.00000000

CHANGE #2 TYP:0 CLS:24 AFN:3 DBA:0x00c1a662 OBJ:4294967295 SCN:0x0000.04fd3150 SEQ:9 OP:5.1 ENC:0 RBL:0

ktudb redo: siz: 168 spc: 2698 flg: 0x0012 seq: 0x02f9 rec: 0x27

xid: 0x0004.014.0000708a

ktubl redo: slt: 20 rci: 0 opc: 11.1 [objn: 91780 objd: 91780 tsn: 4]

Undo type: Regular undo Begin trans Last buffer split: No

Temp Object: No

Tablespace Undo: No

0x00000000 prev ctl uba: 0x00c1a662.02f9.1e

prev ctl max cmt scn: 0x0000.04fd205c prev tx cmt scn: 0x0000.04fd29f4

txn start scn: 0xffff.ffffffff logon user: 84 prev brb: 12691023 prev bcl: 0 BuExt idx: 0 flg2: 0

KDO undo record:

KTB Redo

op: 0x03 ver: 0x01

compat bit: 4 (post-11) padding: 1

op: Z

Array Update of 1 rows:

tabn: 0 slot: 0(0x0) flag: 0x2c lock: 0 ckix: 0

ncol: 2 nnew: 1 size: 0

KDO Op code: 21 row dependencies Disabled

xtype: XAxtype KDO_KDOM2 flags: 0x00000080 bdba: 0x01000a7f hdba: 0x01000a7a

itli: 2 ispac: 0 maxfr: 4858

vect = 3

col 1: [ 5] 61 61 61 61 61

CHANGE #3 TYP:2 CLS:1 AFN:4 DBA:0x01000a7f OBJ:91780 SCN:0x0000.04fd1dca SEQ:1 OP:11.19 ENC:0 RBL:0

KTB Redo

op: 0x11 ver: 0x01

compat bit: 4 (post-11) padding: 1

op: F xid: 0x0004.014.0000708a uba: 0x00c1a662.02f9.27

Block cleanout record, scn: 0x0000.04fd31be ver: 0x01 opt: 0x02, entries follow...

itli: 1 flg: 2 scn: 0x0000.04fd1dca

Array Update of 1 rows:

tabn: 0 slot: 0(0x0) flag: 0x2c lock: 2 ckix: 0

ncol: 2 nnew: 1 size: 0

KDO Op code: 21 row dependencies Disabled

xtype: XAxtype KDO_KDOM2 flags: 0x00000080 bdba: 0x01000a7f hdba: 0x01000a7a

itli: 2 ispac: 0 maxfr: 4858

vect = 3

col 1: [ 5] 41 41 41 41 41

REDO RECORD - Thread:1 RBA: 0x000006.0000000c.0010 LEN: 0x016c VLD: 0x05

SCN: 0x0000.04fd31c9 SUBSCN: 1 11/06/2016 05:06:42

CHANGE #1 TYP:0 CLS:24 AFN:3 DBA:0x00c1a662 OBJ:4294967295 SCN:0x0000.04fd31be SEQ:1 OP:5.1 ENC:0 RBL:0

ktudb redo: siz: 124 spc: 2528 flg: 0x0022 seq: 0x02f9 rec: 0x28

xid: 0x0004.014.0000708a

ktubu redo: slt: 20 rci: 39 opc: 11.1 objn: 91780 objd: 91780 tsn: 4

Undo type: Regular undo Undo type: Last buffer split: No

Tablespace Undo: No

0x00000000

KDO undo record:

KTB Redo

op: 0x02 ver: 0x01

compat bit: 4 (post-11) padding: 1

op: C uba: 0x00c1a662.02f9.27

Array Update of 1 rows:

tabn: 0 slot: 1(0x1) flag: 0x2c lock: 0 ckix: 0

ncol: 2 nnew: 1 size: 0

KDO Op code: 21 row dependencies Disabled

xtype: XAxtype KDO_KDOM2 flags: 0x00000080 bdba: 0x01000a7f hdba: 0x01000a7a

itli: 2 ispac: 0 maxfr: 4858

vect = 3

col 1: [ 5] 62 62 62 62 62

CHANGE #2 TYP:0 CLS:1 AFN:4 DBA:0x01000a7f OBJ:91780 SCN:0x0000.04fd31be SEQ:1 OP:11.19 ENC:0 RBL:0 //OP:11.19 更新数据块

KTB Redo

op: 0x02 ver: 0x01

compat bit: 4 (post-11) padding: 1

op: C uba: 0x00c1a662.02f9.28

Array Update of 1 rows:

tabn: 0 slot: 1(0x1) flag: 0x2c lock: 2 ckix: 0

ncol: 2 nnew: 1 size: 0

KDO Op code: 21 row dependencies Disabled

xtype: XAxtype KDO_KDOM2 flags: 0x00000080 bdba: 0x01000a7f hdba: 0x01000a7a

itli: 2 ispac: 0 maxfr: 4858

vect = 3

col 1: [ 5] 42 42 42 42 42

REDO RECORD - Thread:1 RBA: 0x000006.0000000c.017c LEN: 0x0060 VLD: 0x01

SCN: 0x0000.04fd31ca SUBSCN: 1 11/06/2016 05:06:42

CHANGE #1 TYP:0 CLS:23 AFN:3 DBA:0x00c000b0 OBJ:4294967295 SCN:0x0000.04fd31be SEQ:1 OP:5.4 ENC:0 RBL:0 //提交事务

ktucm redo: slt: 0x0014 sqn: 0x0000708a srt: 0 sta: 9 flg: 0x2 ktucf redo: uba: 0x00c1a662.02f9.28 ext: 31 spc: 2402 fbi: 0

END OF REDO DUMP

----- Redo read statistics for thread 1 -----

Read rate (SYNC): 5Kb in 0.01s => 0.54 Mb/sec

Total redo bytes: 5Kb Longest record: 0Kb, moves: 0/14 moved: 0Mb (0%)

Longest LWN: 1Kb, reads: 5

Last redo scn: 0x0000.04fd31ca (83702218)

Change vector header moves = 0/27 (0%)

----------------------------------------------

总结：

IMU模式下：日志一次性写入，一个事务对应一条日志记录，先写入事务更改前的所有旧值，后写入更新后的新值

非IMU模式下：日志多次写，一个事务中有N次DML操作，则有N条日志记录，每条日志对应一次DML操作，存放该DML操作的旧值和更改后值。

解决问题：减少REDO日志写入次数；快速构造CR块

二、通过实验重现ORA-01555快照过旧的错误，如何避免错误？

重现ORA-01555错误：

SQL> create undo tablespace undo1 datafile '/u01/app/oracle/oradata/edus/undo01.dbf' size 1m;

Tablespace created.

SQL> alter system set undo_retention=1;

System altered.

SQL> var x refcursor

SQL> begin

2 open :x for select * from lvtu;

3 end;

4 /

PL/SQL procedure successfully completed.

SQL> begin

2 for i in 1 .. 20000 loop

3 update lvtu set id=id+1;

4 commit;

5 end loop;

6 end;

7 /

PL/SQL procedure successfully completed.

SQL> print :x

ERROR:

ORA-01555: snapshot too old

如何避免错误：将undo_retention参数设置大点，但会导致UNDO表空间过度扩展，但治标不治本，

从根本就应该从优化SQL语句和数据库对象设计入手，充分利用索引，减少SQL执行时间

3.UNDO的一致性读

SQL> select * from lvtu;

ID NAME

---------- ------------------------------------------------------------

1 DDDDD

2 BBBBB

SQL> var x refcursor;

SQL> exec open:x for select * from lvtu where id=1;

PL/SQL procedure successfully completed.

Commit complete.

SQL> update lvtu set name='AAAAA' where id=1;

1 row updated.

SQL> print x

ID NAME

---------- ------------------------------------------------------------

1 DDDDD

SQL> select dbms_rowid.rowid_relative_fno(rowid),dbms_rowid.rowid_block_number(rowid) from lvtu where id=1;

DBMS_ROWID.ROWID_RELATIVE_FNO(ROWID) DBMS_ROWID.ROWID_BLOCK_NUMBER(ROWID)

------------------------------------ ------------------------------------

4                                 2687

另一会话：

SQL> select addr,xid,xidusn,xidslot,xidsqn,ubafil,ubablk,ubasqn from v$transaction;

ADDR             XID                  XIDUSN    XIDSLOT     XIDSQN     UBAFIL

---------------- ---------------- ---------- ---------- ---------- ----------

UBABLK     UBASQN

---------- ----------

00000000951B0FF0 0500120027730000          5         18      29479          3

91676        781

SQL> alter system checkpoint;

System altered.

SQL> alter system dump datafile 4 block 2687;

System altered.

SQL> select * from  v$diag_info where name like '%Default%';

INST_ID

----------

NAME

--------------------------------------------------------------------------------

VALUE

--------------------------------------------------------------------------------

1

Default Trace File

/u01/oracle/diag/rdbms/edus/edus/trace/edus_ora_14202.trc

Itl           Xid                  Uba         Flag  Lck        Scn/Fsc

0x01   0x0005.012.00007327  0x00c1661c.030d.1c  ----    1  fsc 0x0000.00000000   //未有明确提交标记，XID,通过事务表发现未提交，可以根据UBA(3号文件91676块第28条记录)，往前SCN

0x02   0x0009.00c.00007259  0x00c08040.028f.11  C---    0  scn 0x0000.04fd42a5

bdba: 0x01000a7f

data_block_dump,data header at 0x2ab3be5aea64

===============

tsiz: 0x1f98

hsiz: 0x16

pbl: 0x2ab3be5aea64

76543210

flag=--------

ntab=1

nrow=2

frre=-1

fsbo=0x16

fseo=0x1f80

avsp=0x1f6a

tosp=0x1f6a

0xe:pti[0]      nrow=2  offs=0

0x12:pri[0]     offs=0x1f8c

0x14:pri[1]     offs=0x1f80

block_row_dump:

tab 0, row 0, @0x1f8c

tl: 12 fb: --H-FL-- lb: 0x1  cc: 2

col  0: [ 2]  c1 02

col  1: [ 5]  41 41 41 41 41    //修改未提交的数据

tab 0, row 1, @0x1f80

tl: 12 fb: --H-FL-- lb: 0x0  cc: 2

col  0: [ 2]  c1 03

col  1: [ 5]  42 42 42 42 42

第二次DUMP

SQL> alter system dump datafile 3 block 91676;

System altered.

SQL> select * from  v$diag_info where name like '%Default%';

INST_ID

----------

NAME

--------------------------------------------------------------------------------

VALUE

--------------------------------------------------------------------------------

1

Default Trace File

/u01/oracle/diag/rdbms/edus/edus/trace/edus_ora_14423.trc

*-----------------------------

* Rec #0x1c  slt: 0x12  objn: 91780(0x00016684)  objd: 91780  tblspc: 4(0x00000004)

*       Layer:  11 (Row)   opc: 1   rci 0x00

Undo type:  Regular undo    Begin trans    Last buffer split:  No

Temp Object:  No

Tablespace Undo:  No

rdba: 0x00000000Ext idx: 0

flg2: 0

*-----------------------------

uba: 0x00c1661c.030d.19 ctl max scn: 0x0000.04fd3c64 prv tx scn: 0x0000.04fd3c6d

txn start scn: scn: 0x0000.04fd42b8 logon user: 84

prev brb: 12674585 prev bcl: 0

KDO undo record:

KTB Redo

op: 0x04  ver: 0x01

compat bit: 4 (post-11) padding: 1

op: L  itl: xid:  0x0009.000.00007259 uba: 0x00c08040.028f.10

flg: C---    lkc:  0     scn: 0x0000.04fd4272   //该UNDO记录关联的事务槽信息，FLG:已经提交，对比SCN，发会该SCN与SELECT语发出的SCN最相近

Array Update of 1 rows:

tabn: 0 slot: 0(0x0) flag: 0x2c lock: 0 ckix: 0

ncol: 2 nnew: 1 size: 0

KDO Op code:  21 row dependencies Disabled

xtype: XAxtype KDO_KDOM2 flags: 0x00000080  bdba: 0x01000a7f  hdba: 0x01000a7a

itli: 1  ispac: 0  maxfr: 4858

vect = 3

col  1: [ 5]  44 44 44 44 44  //更新为AAAAA前的旧值，DDDDDD,当前事务的相关旧值

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